A castrato is a male singer who underwent castration before puberty in order to retain singing voice equivalent to that of a soprano, mezzo-soprano, or contralto. The voice can also occur in one who, due to an endocrinological condition, never reaches sexual maturity.

A eunuch is a male who has been castrated. Throughout history, castration often served a specific social function. The earliest records for intentional castration to produce eunuchs are from the Sumerian city of Lagash in the 2nd millennium BCE. Over the millennia since, they have performed a wide variety of functions in many different cultures: courtiers or equivalent domestics, for espionage or clandestine operations, castrato singers, concubines or sexual partners, religious specialists, soldiers, royal guards, government officials, and guardians of women or harem servants.